WASHINGTON — Criminal groups and terrorists north of the border are borrowing a page from the Mexican drug cartel playbook and buying weapons smuggled from the U.S. that are generally unavailable in Canada.

Though the numbers are small compared to the southbound flow of guns to Mexico, U.S. gun traffickers are using similar methods to ferry guns northward.

They hire "straw" purchasers to buy guns in Florida, Alabama, Ohio, Michigan and other states, and send them over border crossings that include Buffalo, Detroit and Washington state.

Canadian gangs exchange highly potent hydroponic marijuana or drugs like Ecstasy for handguns.

"For us, it's a river of guns flowing north," said David Miller, former mayor of Toronto. "'If the traffic were going the other way, you'd see members of Congress saying Canada is exporting terror to the U.S."

From 2007 through 2011, Canada submitted 6,574 guns to the Bureau of Alcohol, Tobacco, Firearms and Explosives for tracing — a fraction of the 99,000 guns Mexico asked ATF to trace.

Virtually all of the guns recovered in Canada were traced to U.S. sources, with just over half linked to a retail purchase in the U.S. By contrast, ATF data showed just over two-thirds of guns from Mexico were traced to U.S. sources — a U.S. manufacturer or importer — and just under one-third were linked to a U.S. retail purchase.

There are stark differences. Canada is relatively tranquil, while Mexico is awash in guns and cartel violence.

Mexican drug cartels prefer military-style semiautomatic rifles like the AK-47 and AR-15, while Canadian counterparts primarily want handguns, which are heavily restricted under Canadian law. Canada has gun registration and licensing; Mexico has neither.

But there are similarities too, including the comparative ease of gun-purchasing in the U.S., drug traffickers' desire to protect turf and limit competition, and a lengthy, easily penetrated border.

Canadian drug rings range from Asian ethnic groups operating primarily in British Columbia to motorcycle gangs and traditional Mafia-type rings in Ontario and Quebec.

Gang-related violence, once a rarity in Canada, is on the rise. In 2005 — "the year of the gun" — Toronto had 52 gun homicides. Toronto police reported that of 181 crime guns they confiscated and traced to a retail sale, two-thirds — 120 — were from the U.S.

ATF officials are loath to attribute Canadian violence entirely to U.S. guns.

"Yes, guns do come from the U.S., no doubt about it," said Regina Lombardo, the agency's attache in Toronto.

However, "we don't know the totality of all weapons recovered in the entire country of Canada."

Canadian law enforcement seized nearly 110,000 firearms over the past four years and fielded at least 439,000 gun-trace requests from 2008 through 2011, said Royal Canadian Mounted Police spokeswoman Julie Gagnon. But many of the seizures and traces were not for guns used in crimes but rather for violations of gun licensing and registration laws, she added.

Because of its tough gun laws, New York state is more of a way station than a source for guns bound for Canada.

Last year, the U.S. Drug Enforcement Administration arrested a drug courier in Syracuse, who was about to take a load of 17 handguns to Canada, said James Burns, the Albany-based DEA agent in charge of New York-Canada border investigations. The guns had been transported from Louisiana.

ATF and ICE agents in 2007 broke up a smuggling ring that used straw purchasers to buy guns in Florida, Georgia and Alabama in exchange for ecstasy pills. The gang then transported the guns to Canada in hidden compartments of rental cars.

Canadian border guards stopped one of the cars at the Peace Bridge between Buffalo and Fort Erie, Ontario, and found seven handguns and half a pound of cocaine.

Terrorists too have gotten in on the act. The Toronto 18 plot to blow up that city's stock exchange and other buildings began to unravel in 2005 when Canadian border guards stopped two Somali immigrants on the Peace Bridge and found three loaded handguns they had purchased in Columbus, Ohio. Two of the guns were taped to the thighs of the group's chief gunrunner, Ali Dirie.

Guns traced to a trafficking ring's purchase of 500 weapons in Kentucky were implicated in the shooting deaths of eight Bandito motorcycle gang members and a shootout with police after a jewelry store holdup, both in Ontario. The ringleader, Ricardo Tolliver, had exchanged the guns for marijuana. He was convicted in federal court in 2009 and sentenced to 32 years in prison.

"Handguns are strictly controlled in Canada, so that's what creates the market," said Wendy Cukier, a professor at Ryerson University in Toronto and president of the Coalition for Gun Control. With American weapons abundantly available, "it stands to reason the leakage of the domestic supply of U.S. guns is going to create problems in other countries."

ATF, besieged by accusations of wrongdoing in Operation Fast & Furious on the Southwest border, is not anxious to engage in any finger-pointing. In Fast & Furious, Phoenix-based ATF agents used watch-and-wait tactics on cartel-linked gun purchasers but then lost track of over 2,000 weapons once they were transported to Mexico.

But unlike the Southwest border, where relations with Mexican authorities have been strained by a long history of corruption in Mexico, the Northern border is a model of law enforcement cooperation, U.S. officials say.

"We are working side by side with Canadian officers (to) let them know that if guns are sourced to the U.S., we are committed to cutting off that pipeline," Lombardo said.